Block allocation for persistent memory during aggregate transition

ABSTRACT

Techniques are provided for block allocation for persistent memory during aggregate transition. In a high availability pair including first and second nodes, the first node makes a determination that control of a first aggregate is to transition from the first node to the second node. A portion of available free storage space is allocated from a first persistent memory of the first node as allocated pages within the first persistent memory. Metadata information for the allocated pages is updated with an identifier of the first aggregate to create updated metadata information reserving the allocated pages for the first aggregate. The updated metadata information is mirrored to the second node, so that the second node also reserves those pages. Control of the first aggregate is transitioned to the second node. As a result, the nodes do not attempt allocating the same free pages to different aggregates during a transition.

RELATED APPLICATION

This application claims priority to and is a continuation of U.S. patentapplication Ser. No. 16/911,425, titled BLOCK ALLOCATION FOR PERSISTENTMEMORY DURING AGGREGATE TRANSITION” and filed on Jun. 25, 2020, which isincorporated herein by reference.

BACKGROUND

A computing environment may host one or more nodes, such as servers,virtual machines, computing devices, etc., for storing data on behalf ofclients. The nodes may be deployed in a manner that provides highavailability, data redundancy, and/or other storage features. Forexample, a first node may host one or more aggregates within which datais stored, such as a first aggregate used to store data on behalf of afirst client. The first node may store at least some data of the firstaggregate within a first persistent memory of the first node. A secondnode may also host one or more aggregates within which data is stored,such as a second aggregate used to store data on behalf of a secondclient. The second node may store at least some data of the secondaggregate within a second persistent memory of the second node.

The first node and the second node may be configured as a node pairing(e.g., a high availability node pairing) configured to provide highavailability and/or failover functionality. For example, if one of thenodes fails, then the surviving node can provide clients with failoveraccess to their data in place of the failed node. This can beaccomplished by mirroring data between the persistent memories of thenodes so that the surviving node has an up-to-date copy of data from apersistent memory of the failed node. In this way, the surviving nodecan provide clients with up-to-date data that was previously accessibleto the clients through the failed node.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example computing environmentin which an embodiment may be implemented.

FIG. 2 is a block diagram illustrating a network environment withexemplary node computing devices.

FIG. 3 is a block diagram illustrating an exemplary node computingdevice.

FIG. 4 is a flow chart illustrating an example method for blockallocation for persistent memory during aggregate transition.

FIG. 5A is a block diagram illustrating an example system for blockallocation for persistent memory during aggregate transition, where anode (A) and a node (B) are operating under normal operation.

FIG. 5B is a block diagram illustrating an example system for blockallocation for persistent memory during aggregate transition, where anode (B) fails.

FIG. 5C is a block diagram illustrating an example system for blockallocation for persistent memory during aggregate transition, where anode (A) takes over an aggregate (B1) and an aggregate (B2).

FIG. 5D is a block diagram illustrating an example system for blockallocation for persistent memory during aggregate transition, where anode (B) recovers from a failure and a node (A) updates metadatainformation for an aggregate (B1).

FIG. 5E is a block diagram illustrating an example system for blockallocation for persistent memory during aggregate transition, where anode (A) gives back an aggregate (B1) to a node (B).

FIG. 5F is a block diagram illustrating an example system for blockallocation for persistent memory during aggregate transition, where anode (A) updates metadata information for an aggregate (B2).

FIG. 5G is a block diagram illustrating an example system for blockallocation for persistent memory during aggregate transition, where anode (A) gives back an aggregate (B2) to a node (B).

FIG. 6 is an example of a computer readable medium in which anembodiment may be implemented.

DETAILED DESCRIPTION

Some examples of the claimed subject matter are now described withreference to the drawings, where like reference numerals are generallyused to refer to like elements throughout. In the following description,for purposes of explanation, numerous specific details are set forth inorder to provide an understanding of the claimed subject matter. It maybe evident, however, that the claimed subject matter may be practicedwithout these specific details. Nothing in this detailed description isadmitted as prior art.

A first node may be implemented as a computing device, a server, anon-premise device, a virtual machine, hardware, software, or combinationthereof. The first node may store client data within one or moreaggregates, such as a first aggregate and a second aggregate. In orderto provide high availability and redundancy, the first node may bepaired with a second node. The second node may also store client datawithin one or more aggregates, such as a third aggregate and a fourthaggregate. Data is mirrored between the first node and the second node,such as between a first persistent memory of the first node and a secondpersistent memory of the second node, so that both nodes have up-to-datedata of the other node.

For example, the first persistent memory may be partitioned into a firstlocal partition into which data of the first aggregate and the secondaggregate may be stored. The first persistent memory may be partitionedinto a first remote partition into which data of the third aggregate andthe fourth aggregate is mirrored from the second persistent memory ofthe second node (e.g., from a second local partition of the secondpersistent memory). Similarly, the second persistent memory may bepartitioned into the second local partition into which data of the thirdaggregate and the fourth aggregate may be stored. The second persistentmemory may be partitioned into a second remote partition into which dataof the first aggregate and second aggregate is mirrored from the firstlocal partition of the first persistent memory of the first node.

Because data is mirrored between the persistent memories of the nodes,the nodes may be capable of providing takeover and givebackfunctionality. For example, if one of the nodes fails, then thesurviving node can take over aggregates of the failed node usingup-to-date data within the remote partition of the persistent memory ofthe surviving node. Once the failed node has recovered, the survivingnode can give back control of the taken over aggregates to the recoverednode.

For example, the first node may fail, and the second node may take overthe first and second aggregates from the first node. The second node mayscan the second remote partition of the second persistent memory,corresponding to the mirrored data of the first and second aggregates,to build a free pages list of free pages within the second remotepartition that can be subsequently allocated to store data directed tothe first and second aggregates. In this way, the second node willservice I/O directed to the first and second aggregates using the secondremote partition. Once the first node recovers from the failure, thesecond node may perform a giveback procedure to return the first andsecond aggregates to the first node one at a time. Also, once the firstnode has recovered, a resynchronization procedure is performed to copydata of the second remote partition of the second node into the firstlocal partition of the first node in order to mirror changes to thefirst and second aggregates made while the first node had failed and thesecond node had taken over control of the first and second aggregates.Furthermore, the second node actively mirrors I/O data, directed to thefirst and second aggregates and being processed by the second node usingthe second remote partition, to the first local partition of the firstnode.

In certain situations, data corruption can result during the transitionof aggregates between nodes, such as during a giveback procedure or aplanned takeover. Continuing with the example, if for some reason merelycontrol of the first aggregate is transferred back to the first node andcontrol of the second aggregate is retained by the second node, thendata corruption/loss can occur. This is because the second remotepartition of the second persistent memory of the second node is kept asan exact mirror of the first local partition of the first persistentmemory of the first node. However, the first node is serving I/Odirected to the first aggregate using the first local partition and thesecond node is serving I/O directed to the second aggregate using thesecond remote partition. It is possible that the first node, servicingI/O to the first aggregate using the first local partition, may write toa page block number (e.g., a free page within the first local partitioncorresponding to page block number 500) that is the same page blocknumber to which the second node is writing to while servicing I/O to thesecond aggregate using the second remote partition (e.g., a free pagewithin the second remote partition corresponding to the page blocknumber 500). Data corruption occurs in this example because only oneversion of the data may be persisted (data loss) once the first localpartition and the second remote partition are mirrored to one another soas to prevent a mismatch of data where page block number 500 of thefirst local partition has different data than page block number 500 ofthe second remote partition (data corruption).

Accordingly, as provided herein, data corruption and data loss isavoided when transitioning control of aggregates between nodes during agiveback of aggregates between the nodes, a takeover (planned takeover)of aggregates between the nodes, or any other scenario where control ofone or more aggregates is being transitioned between nodes. In anembodiment, when the second node determines that control of an aggregate(e.g., the first aggregate or the second aggregate originallyowned/controlled by the first node) is to be given back from the secondnode to the first node, the second node allocates a portion of availablefree storage space within the second remote partition of the secondpersistent memory of the second node. The portion of available freestorage space comprises a set of free pages within the second remotepartition of the second persistent memory of the second node that arenow being allocated/reserved for subsequent use when processing and/ormirroring data of I/O directed to the aggregate. The set of free pagesare removed from a free pages list maintained by the second node for thesecond persistent memory, such as where page block numbers used to indexthe set of free pages are removed from the free pages list.

The second node updates metadata information, corresponding to thesecond persistent memory, for the set of free pages with an identifierof the aggregate to create updated metadata information reserving theallocated pages for the aggregate. For example, the page block numbersused to index the set of free pages are tagged with the identifier ofthe aggregate so that the updated metadata information specifies thatthose page block numbers are being reserved for the aggregate. Thesecond node transmits the updated metadata information to the firstnode.

The first node uses the updated metadata information to build a freepages list of free pages for the aggregate to use from the first localpartition. The first node builds the free pages list by traversing theupdated metadata information and by adding entries tagged with theidentifier of the aggregate to the free pages list. Any subsequentallocations of free pages from the first local partition to store I/Odirected to the aggregate and processed by the first node will use freepages within the free pages list, corresponding to those pages that werepreviously reserved and available within the second remote partition ofthe second persistent memory of the second node. In an embodiment, thefree pages list is used until all aggregates whose control are to betransitioned have successfully been transitioned from the second node tothe first node. In this way, the first local partition and the secondremote partition implement a temporary soft partition of free pagesreserved for the aggregate during a transition window of transitioningcontrol of the aggregates. The second node then transfers control of theaggregate to the first node.

If for some reason control of the aggregate does not transfer to thefirst node, then both the first node and the second node have the samefree pages lists to use for respectively reserving pages within thefirst local partition and the second remote partition for subsequentallocation for the aggregate (e.g., the aggregate whose control wasretained by the second node) and another aggregate (e.g., an aggradewhose control was passed to the first node) even though the second nodewill continue to process the I/O directed to the partition based uponretaining control of the partition. In this way, data corruption/loss isavoided because the same free pages (the same page block numbers) arereserved by both nodes for the partition. For example, control of afirst aggregate may be retained by the second node (e.g., due to afailure to transition control of the first aggregate) but control of asecond aggregate may be successfully transferred back to the first node.Without the reservation of the same free pages for storing data of thefirst aggregate, data corruption/loss could otherwise occur where thefirst node tries to allocate a free page for the second aggregate thatis the same as a free page being allocated by the second node for thefirst aggregate.

This partitioning of the first persistent memory and the secondpersistent memory may be performed during a transition window oftransitioning control of aggregates between nodes. This partitioning maybe referred to as a soft partition because it may be determined inreal-time during the transition window as opposed to being a hard setpartition. After the transition window, the soft partition may beremoved such that there is normally no partition of storage betweenaggregates controlled by the same node (e.g., no partition within alocal partition of persistent memory and/or no partition within a remotepartition of the persistent memory), which provides improved flexibilityfor managing persistent memories of the nodes. Furthermore, the nodes donot have to maintain a centralized free list that is updated usinginter-node communication, which simplifies the ability to avoid datacorruption and loss, along with reducing inter-node communication forimproving/reducing bandwidth overhead.

FIG. 1 is a diagram illustrating an example operating environment 100 inwhich an embodiment of the techniques described herein may beimplemented. In one example, the techniques described herein may beimplemented within a client device 128, such as a laptop, a tablet, apersonal computer, a mobile device, a server, a virtual machine, awearable device, etc. In another example, the techniques describedherein may be implemented within one or more nodes, such as a first node130 and/or a second node 132 within a first cluster 134, a third node136 within a second cluster 138, etc. A node may comprise a storagecontroller, a server, an on-premise device, a virtual machine such as astorage virtual machine, hardware, software, or combination thereof. Theone or more nodes may be configured to manage the storage and access todata on behalf of the client device 128 and/or other client devices. Inanother example, the techniques described herein may be implementedwithin a distributed computing platform 102 such as a cloud computingenvironment (e.g., a cloud storage environment, a multi-tenant platform,a hyperscale infrastructure comprising scalable server architectures andvirtual networking, etc.) configured to manage the storage and access todata on behalf of client devices and/or nodes.

In yet another example, at least some of the techniques described hereinare implemented across one or more of the client device 128, the one ormore nodes 130, 132, and/or 136, and/or the distributed computingplatform 102. For example, the client device 128 may transmitoperations, such as data operations to read data and write data andmetadata operations (e.g., a create file operation, a rename directoryoperation, a resize operation, a set attribute operation, etc.), over anetwork 126 to the first node 130 for implementation by the first node130 upon storage. The first node 130 may store data associated with theoperations within volumes or other data objects/structures hosted withinlocally attached storage, remote storage hosted by other computingdevices accessible over the network 126, storage provided by thedistributed computing platform 102, etc. The first node 130 mayreplicate the data and/or the operations to other computing devices,such as to the second node 132, the third node 136, a storage virtualmachine executing within the distributed computing platform 102, etc.,so that one or more replicas of the data are maintained. For example,the third node 136 may host a destination storage volume that ismaintained as a replica of a source storage volume of the first node130. Such replicas can be used for disaster recovery and failover.

In an embodiment, the techniques described herein are implemented by astorage operating system or are implemented by a separate module thatinteracts with the storage operating system. The storage operatingsystem may be hosted by the client device, 128, a node, the distributedcomputing platform 102, or across a combination thereof. In an example,the storage operating system may execute within a storage virtualmachine, a hyperscaler, or other computing environment. The storageoperating system may implement a one or more file systems to logicallyorganize data within storage devices as one or more storage objects andprovide a logical/virtual representation of how the storage objects areorganized on the storage devices (e.g., a file system tailored forblock-addressable storage, a file system tailored for byte-addressablestorage such as persistent memory). A storage object may comprise anylogically definable storage element stored by the storage operatingsystem (e.g., a volume stored by the first node 130, a cloud objectstored by the distributed computing platform 102, etc.). Each storageobject may be associated with a unique identifier that uniquelyidentifies the storage object. For example, a volume may be associatedwith a volume identifier uniquely identifying that volume from othervolumes. The storage operating system also manages client access to thestorage objects.

The storage operating system may implement a file system for logicallyorganizing data. For example, the storage operating system may implementa write anywhere file layout for a volume where modified data for a filemay be written to any available location as opposed to a write-in-placearchitecture where modified data is written to the original location,thereby overwriting the previous data. In an example, the file systemmay be implemented through a file system layer that stores data of thestorage objects in an on-disk format representation that is block-based(e.g., data is stored within 4 kilobyte blocks and inodes are used toidentify files and file attributes such as creation time, accesspermissions, size and block location, etc.).

In an example, deduplication may be implemented by a deduplicationmodule associated with the storage operating system. Deduplication isperformed to improve storage efficiency. One type of deduplication isinline deduplication that ensures blocks are deduplicated before beingwritten to a storage device. Inline deduplication uses a data structure,such as an incore hash store, which maps fingerprints of data to datablocks of the storage device storing the data. Whenever data is to bewritten to the storage device, a fingerprint of that data is calculatedand the data structure is looked up using the fingerprint to findduplicates (e.g., potentially duplicate data already stored within thestorage device). If duplicate data is found, then the duplicate data isloaded from the storage device and a byte by byte comparison may beperformed to ensure that the duplicate data is an actual duplicate ofthe data to be written to the storage device. If the data to be writtenis a duplicate of the loaded duplicate data, then the data to be writtento disk is not redundantly stored to the storage device. Instead, apointer or other reference is stored in the storage device in place ofthe data to be written to the storage device. The pointer points to theduplicate data already stored in the storage device. A reference countfor the data may be incremented to indicate that the pointer nowreferences the data. If at some point the pointer no longer referencesthe data (e.g., the deduplicated data is deleted and thus no longerreferences the data in the storage device), then the reference count isdecremented. In this way, inline deduplication is able to deduplicatedata before the data is written to disk. This improves the storageefficiency of the storage device.

Background deduplication is another type of deduplication thatdeduplicates data already written to a storage device. Various types ofbackground deduplication may be implemented. In an example of backgrounddeduplication, data blocks that are duplicated between files arerearranged within storage units such that one copy of the data occupiesphysical storage. References to the single copy can be inserted into afile system structure such that all files or containers that contain thedata refer to the same instance of the data. Deduplication can beperformed on a data storage device block basis. In an example, datablocks on a storage device can be identified using a physical volumeblock number. The physical volume block number uniquely identifies aparticular block on the storage device. Additionally, blocks within afile can be identified by a file block number. The file block number isa logical block number that indicates the logical position of a blockwithin a file relative to other blocks in the file. For example, fileblock number 0 represents the first block of a file, file block number 1represents the second block, etc. File block numbers can be mapped to aphysical volume block number that is the actual data block on thestorage device. During deduplication operations, blocks in a file thatcontain the same data are deduplicated by mapping the file block numberfor the block to the same physical volume block number, and maintaininga reference count of the number of file block numbers that map to thephysical volume block number. For example, assume that file block number0 and file block number 5 of a file contain the same data, while fileblock numbers 1-4 contain unique data. File block numbers 1-4 are mappedto different physical volume block numbers. File block number 0 and fileblock number 5 may be mapped to the same physical volume block number,thereby reducing storage requirements for the file. Similarly, blocks indifferent files that contain the same data can be mapped to the samephysical volume block number. For example, if file block number 0 offile A contains the same data as file block number 3 of file B, fileblock number 0 of file A may be mapped to the same physical volume blocknumber as file block number 3 of file B.

In another example of background deduplication, a changelog is utilizedto track blocks that are written to the storage device. Backgrounddeduplication also maintains a fingerprint database (e.g., a flatmetafile) that tracks all unique block data such as by tracking afingerprint and other filesystem metadata associated with block data.Background deduplication can be periodically executed or triggered basedupon an event such as when the changelog fills beyond a threshold. Aspart of background deduplication, data in both the changelog and thefingerprint database is sorted based upon fingerprints. This ensuresthat all duplicates are sorted next to each other. The duplicates aremoved to a dup file. The unique changelog entries are moved to thefingerprint database, which will serve as duplicate data for a nextdeduplication operation. In order to optimize certain filesystemoperations needed to deduplicate a block, duplicate records in the dupfile are sorted in certain filesystem sematic order (e.g., inode numberand block number). Next, the duplicate data is loaded from the storagedevice and a whole block byte by byte comparison is performed to makesure duplicate data is an actual duplicate of the data to be written tothe storage device. After, the block in the changelog is modified topoint directly to the duplicate data as opposed to redundantly storingdata of the block.

In an example, deduplication operations performed by a datadeduplication layer of a node can be leveraged for use on another nodeduring data replication operations. For example, the first node 130 mayperform deduplication operations to provide for storage efficiency withrespect to data stored on a storage volume. The benefit of thededuplication operations performed on first node 130 can be provided tothe second node 132 with respect to the data on first node 130 that isreplicated to the second node 132. In some aspects, a data transferprotocol, referred to as the LRSE (Logical Replication for StorageEfficiency) protocol, can be used as part of replicating consistencygroup differences from the first node 130 to the second node 132. In theLRSE protocol, the second node 132 maintains a history buffer that keepstrack of data blocks that it has previously received. The history buffertracks the physical volume block numbers and file block numbersassociated with the data blocks that have been transferred from firstnode 130 to the second node 132. A request can be made of the first node130 to not transfer blocks that have already been transferred. Thus, thesecond node 132 can receive deduplicated data from the first node 130,and will not need to perform deduplication operations on thededuplicated data replicated from first node 130.

In an example, the first node 130 may preserve deduplication of datathat is transmitted from first node 130 to the distributed computingplatform 102. For example, the first node 130 may create an objectcomprising deduplicated data. The object is transmitted from the firstnode 130 to the distributed computing platform 102 for storage. In thisway, the object within the distributed computing platform 102 maintainsthe data in a deduplicated state. Furthermore, deduplication may bepreserved when deduplicated data is transmitted/replicated/mirroredbetween the client device 128, the first node 130, the distributedcomputing platform 102, and/or other nodes or devices.

In an example, compression may be implemented by a compression moduleassociated with the storage operating system. The compression module mayutilize various types of compression techniques to replace longersequences of data (e.g., frequently occurring and/or redundantsequences) with shorter sequences, such as by using Huffman coding,arithmetic coding, compression dictionaries, etc. For example, anuncompressed portion of a file may comprise “ggggnnnnnnqqqqqqqqqq”,which is compressed to become “4g6n10q”. In this way, the size of thefile can be reduced to improve storage efficiency. Compression may beimplemented for compression groups. A compression group may correspondto a compressed group of blocks. The compression group may berepresented by virtual volume block numbers. The compression group maycomprise contiguous or non-contiguous blocks.

Compression may be preserved when compressed data istransmitted/replicated/mirrored between the client device 128, a node,the distributed computing platform 102, and/or other nodes or devices.For example, an object may be created by the first node 130 to comprisecompressed data. The object is transmitted from the first node 130 tothe distributed computing platform 102 for storage. In this way, theobject within the distributed computing platform 102 maintains the datain a compressed state.

In an example, various types of synchronization may be implemented by asynchronization module associated with the storage operating system. Inan example, synchronous replication may be implemented, such as betweenthe first node 130 and the second node 132. It may be appreciated thatthe synchronization module may implement synchronous replication betweenany devices within the operating environment 100, such as between thefirst node 130 of the first cluster 134 and the third node 136 of thesecond cluster 138 and/or between a node of a cluster and an instance ofa node or virtual machine in the distributed computing platform 102.

As an example, during synchronous replication, the first node 130 mayreceive a write operation from the client device 128. The writeoperation may target a file stored within a volume managed by the firstnode 130. The first node 130 replicates the write operation to create areplicated write operation. The first node 130 locally implements thewrite operation upon the file within the volume. The first node 130 alsotransmits the replicated write operation to a synchronous replicationtarget, such as the second node 132 that maintains a replica volume as areplica of the volume maintained by the first node 130. The second node132 will execute the replicated write operation upon the replica volumeso that the file within the volume and the replica volume comprises thesame data. After, the second node 132 will transmit a success message tothe first node 130. With synchronous replication, the first node 130does not respond with a success message to the client device 128 for thewrite operation until both the write operation is executed upon thevolume and the first node 130 receives the success message that thesecond node 132 executed the replicated write operation upon the replicavolume.

In another example, asynchronous replication may be implemented, such asbetween the first node 130 and the third node 136. It may be appreciatedthat the synchronization module may implement asynchronous replicationbetween any devices within the operating environment 100, such asbetween the first node 130 of the first cluster 134 and the distributedcomputing platform 102. In an example, the first node 130 may establishan asynchronous replication relationship with the third node 136. Thefirst node 130 may capture a baseline snapshot of a first volume as apoint in time representation of the first volume. The first node 130 mayutilize the baseline snapshot to perform a baseline transfer of the datawithin the first volume to the third node 136 in order to create asecond volume within the third node 136 comprising data of the firstvolume as of the point in time at which the baseline snapshot wascreated.

After the baseline transfer, the first node 130 may subsequently createsnapshots of the first volume over time. As part of asynchronousreplication, an incremental transfer is performed between the firstvolume and the second volume. In particular, a snapshot of the firstvolume is created. The snapshot is compared with a prior snapshot thatwas previously used to perform the last asynchronous transfer (e.g., thebaseline transfer or a prior incremental transfer) of data to identify adifference in data of the first volume between the snapshot and theprior snapshot (e.g., changes to the first volume since the lastasynchronous transfer). Accordingly, the difference in data isincrementally transferred from the first volume to the second volume. Inthis way, the second volume will comprise the same data as the firstvolume as of the point in time when the snapshot was created forperforming the incremental transfer. It may be appreciated that othertypes of replication may be implemented, such as semi-sync replication.

In an embodiment, the first node 130 may store data or a portion thereofwithin storage hosted by the distributed computing platform 102 bytransmitting the data within objects to the distributed computingplatform 102. In one example, the first node 130 may locally storefrequently accessed data within locally attached storage. Lessfrequently accessed data may be transmitted to the distributed computingplatform 102 for storage within a data storage tier 108. The datastorage tier 108 may store data within a service data store 120, and maystore client specific data within client data stores assigned to suchclients such as a client (1) data store 122 used to store data of aclient (1) and a client (N) data store 124 used to store data of aclient (N). The data stores may be physical storage devices or may bedefined as logical storage, such as a virtual volume, LUNs, or otherlogical organizations of data that can be defined across one or morephysical storage devices. In another example, the first node 130transmits and stores all client data to the distributed computingplatform 102. In yet another example, the client device 128 transmitsand stores the data directly to the distributed computing platform 102without the use of the first node 130.

The management of storage and access to data can be performed by one ormore storage virtual machines (SVMs) or other storage applications thatprovide software as a service (SaaS) such as storage software services.In one example, an SVM may be hosted within the client device 128,within the first node 130, or within the distributed computing platform102 such as by the application server tier 106. In another example, oneor more SVMs may be hosted across one or more of the client device 128,the first node 130, and the distributed computing platform 102. The oneor more SVMs may host instances of the storage operating system.

In an example, the storage operating system may be implemented for thedistributed computing platform 102. The storage operating system mayallow client devices to access data stored within the distributedcomputing platform 102 using various types of protocols, such as aNetwork File System (NFS) protocol, a Server Message Block (SMB)protocol and Common Internet File System (CIFS), and Internet SmallComputer Systems Interface (iSCSI), and/or other protocols. The storageoperating system may provide various storage services, such as disasterrecovery (e.g., the ability to non-disruptively transition clientdevices from accessing a primary node that has failed to a secondarynode that is taking over for the failed primary node), backup andarchive function, replication such as asynchronous and/or synchronousreplication, deduplication, compression, high availability storage,cloning functionality (e.g., the ability to clone a volume, such as aspace efficient flex clone), snapshot functionality (e.g., the abilityto create snapshots and restore data from snapshots), data tiering(e.g., migrating infrequently accessed data to slower/cheaper storage),encryption, managing storage across various platforms such as betweenon-premise storage systems and multiple cloud systems, etc.

In one example of the distributed computing platform 102, one or moreSVMs may be hosted by the application server tier 106. For example, aserver (1) 116 is configured to host SVMs used to execute applicationssuch as storage applications that manage the storage of data of theclient (1) within the client (1) data store 122. Thus, an SVM executingon the server (1) 116 may receive data and/or operations from the clientdevice 128 and/or the first node 130 over the network 126. The SVMexecutes a storage application and/or an instance of the storageoperating system to process the operations and/or store the data withinthe client (1) data store 122. The SVM may transmit a response back tothe client device 128 and/or the first node 130 over the network 126,such as a success message or an error message. In this way, theapplication server tier 106 may host SVMs, services, and/or otherstorage applications using the server (1) 116, the server (N) 118, etc.

A user interface tier 104 of the distributed computing platform 102 mayprovide the client device 128 and/or the first node 130 with access touser interfaces associated with the storage and access of data and/orother services provided by the distributed computing platform 102. In anexample, a service user interface 110 may be accessible from thedistributed computing platform 102 for accessing services subscribed toby clients and/or nodes, such as data replication services, applicationhosting services, data security services, human resource services,warehouse tracking services, accounting services, etc. For example,client user interfaces may be provided to corresponding clients, such asa client (1) user interface 112, a client (N) user interface 114, etc.The client (1) can access various services and resources subscribed toby the client (1) through the client (1) user interface 112, such asaccess to a web service, a development environment, a human resourceapplication, a warehouse tracking application, and/or other services andresources provided by the application server tier 106, which may usedata stored within the data storage tier 108.

The client device 128 and/or the first node 130 may subscribe to certaintypes and amounts of services and resources provided by the distributedcomputing platform 102. For example, the client device 128 may establisha subscription to have access to three virtual machines, a certainamount of storage, a certain type/amount of data redundancy, a certaintype/amount of data security, certain service level agreements (SLAs)and service level objectives (SLOs), latency guarantees, bandwidthguarantees, access to execute or host certain applications, etc.Similarly, the first node 130 can establish a subscription to haveaccess to certain services and resources of the distributed computingplatform 102.

As shown, a variety of clients, such as the client device 128 and thefirst node 130, incorporating and/or incorporated into a variety ofcomputing devices may communicate with the distributed computingplatform 102 through one or more networks, such as the network 126. Forexample, a client may incorporate and/or be incorporated into a clientapplication (e.g., software) implemented at least in part by one or moreof the computing devices.

Examples of suitable computing devices include personal computers,server computers, desktop computers, nodes, storage servers, nodes,laptop computers, notebook computers, tablet computers or personaldigital assistants (PDAs), smart phones, cell phones, and consumerelectronic devices incorporating one or more computing devicecomponents, such as one or more electronic processors, microprocessors,central processing units (CPU), or controllers. Examples of suitablenetworks include networks utilizing wired and/or wireless communicationtechnologies and networks operating in accordance with any suitablenetworking and/or communication protocol (e.g., the Internet). In usecases involving the delivery of customer support services, the computingdevices noted represent the endpoint of the customer support deliveryprocess, i.e., the consumer's device.

The distributed computing platform 102, such as a multi-tenant businessdata processing platform or cloud computing environment, may includemultiple processing tiers, including the user interface tier 104, theapplication server tier 106, and a data storage tier 108. The userinterface tier 104 may maintain multiple user interfaces, includinggraphical user interfaces and/or web-based interfaces. The userinterfaces may include the service user interface 110 for a service toprovide access to applications and data for a client (e.g., a “tenant”)of the service, as well as one or more user interfaces that have beenspecialized/customized in accordance with user specific requirements(e.g., as discussed above), which may be accessed via one or more APIs.

The service user interface 110 may include components enabling a tenantto administer the tenant's participation in the functions andcapabilities provided by the distributed computing platform 102, such asaccessing data, causing execution of specific data processingoperations, etc. Each processing tier may be implemented with a set ofcomputers, virtualized computing environments such as a storage virtualmachine or storage virtual server, and/or computer components includingcomputer servers and processors, and may perform various functions,methods, processes, or operations as determined by the execution of asoftware application or set of instructions.

The data storage tier 108 may include one or more data stores, which mayinclude the service data store 120 and one or more client data stores122-124. Each client data store may contain tenant-specific data that isused as part of providing a range of tenant-specific business andstorage services or functions, including but not limited to ERP, CRM,eCommerce, Human Resources management, payroll, storage services, etc.Data stores may be implemented with any suitable data storagetechnology, including structured query language (SQL) based relationaldatabase management systems (RDBMS), file systems hosted by operatingsystems, object storage, etc.

The distributed computing platform 102 may be a multi-tenant and serviceplatform operated by an entity in order to provide multiple tenants witha set of business related applications, data storage, and functionality.These applications and functionality may include ones that a businessuses to manage various aspects of its operations. For example, theapplications and functionality may include providing web-based access tobusiness information systems, thereby allowing a user with a browser andan Internet or intranet connection to view, enter, process, or modifycertain types of business information or any other type of information.

A clustered network environment 200 that may implement one or moreaspects of the techniques described and illustrated herein is shown inFIG. 2 . The clustered network environment 200 includes data storageapparatuses 202(1)-202(n) that are coupled over a cluster or clusterfabric 204 that includes one or more communication network(s) andfacilitates communication between the data storage apparatuses202(1)-202(n) (and one or more modules, components, etc. therein, suchas, node computing devices 206(1)-206(n), for example), although anynumber of other elements or components can also be included in theclustered network environment 200 in other examples. This technologyprovides a number of advantages including methods, non-transitorycomputer readable media, and computing devices that implement thetechniques described herein.

In this example, node computing devices 206(1)-206(n) can be primary orlocal storage controllers or secondary or remote storage controllersthat provide client devices 208(1)-208(n) with access to data storedwithin data storage devices 210(1)-210(n) and cloud storage device(s)236 (also referred to as cloud storage node(s)). The node computingdevices 206(1)-206(n) may be implemented as hardware, software (e.g., astorage virtual machine), or a combination thereof.

The data storage apparatuses 202(1)-202(n) and/or node computing devices206(1)-206(n) of the examples described and illustrated herein are notlimited to any particular geographic areas and can be clustered locallyand/or remotely via a cloud network, or not clustered in other examples.Thus, in one example the data storage apparatuses 202(1)-202(n) and/ornode computing device 206(1)-206(n) can be distributed over a pluralityof storage systems located in a plurality of geographic locations (e.g.,located on-premise, located within a cloud computing environment, etc.);while in another example a clustered network can include data storageapparatuses 202(1)-202(n) and/or node computing device 206(1)-206(n)residing in a same geographic location (e.g., in a single on-site rack).

In the illustrated example, one or more of the client devices208(1)-208(n), which may be, for example, personal computers (PCs),computing devices used for storage (e.g., storage servers), or othercomputers or peripheral devices, are coupled to the respective datastorage apparatuses 202(1)-202(n) by network connections 212(1)-212(n).Network connections 212(1)-212(n) may include a local area network (LAN)or wide area network (WAN) (i.e., a cloud network), for example, thatutilize TCP/IP and/or one or more Network Attached Storage (NAS)protocols, such as a Common Internet Filesystem (CIFS) protocol or aNetwork Filesystem (NFS) protocol to exchange data packets, a StorageArea Network (SAN) protocol, such as Small Computer System Interface(SCSI) or Fiber Channel Protocol (FCP), an object protocol, such assimple storage service (S3), and/or non-volatile memory express (NVMe),for example.

Illustratively, the client devices 208(1)-208(n) may be general-purposecomputers running applications and may interact with the data storageapparatuses 202(1)-202(n) using a client/server model for exchange ofinformation. That is, the client devices 208(1)-208(n) may request datafrom the data storage apparatuses 202(1)-202(n) (e.g., data on one ofthe data storage devices 210(1)-210(n) managed by a network storagecontroller configured to process I/O commands issued by the clientdevices 208(1)-208(n)), and the data storage apparatuses 202(1)-202(n)may return results of the request to the client devices 208(1)-208(n)via the network connections 212(1)-212(n).

The node computing devices 206(1)-206(n) of the data storage apparatuses202(1)-202(n) can include network or host nodes that are interconnectedas a cluster to provide data storage and management services, such as toan enterprise having remote locations, cloud storage (e.g., a storageendpoint may be stored within cloud storage device(s) 236), etc., forexample. Such node computing devices 206(1)-206(n) can be attached tothe cluster fabric 204 at a connection point, redistribution point, orcommunication endpoint, for example. One or more of the node computingdevices 206(1)-206(n) may be capable of sending, receiving, and/orforwarding information over a network communications channel, and couldcomprise any type of device that meets any or all of these criteria.

In an example, the node computing devices 206(1) and 206(n) may beconfigured according to a disaster recovery configuration whereby asurviving node provides switchover access to the storage devices210(1)-210(n) in the event a disaster occurs at a disaster storage site(e.g., the node computing device 206(1) provides client device 212(n)with switchover data access to data storage devices 210(n) in the eventa disaster occurs at the second storage site). In other examples, thenode computing device 206(n) can be configured according to an archivalconfiguration and/or the node computing devices 206(1)-206(n) can beconfigured based on another type of replication arrangement (e.g., tofacilitate load sharing). Additionally, while two node computing devicesare illustrated in FIG. 2 , any number of node computing devices or datastorage apparatuses can be included in other examples in other types ofconfigurations or arrangements. In an example, control of aggregates maybe switched between the node computing devices 206(1) and 206(n) in theevent of a disaster or planned takeover. As provided herein, blockallocation for persistent memory during aggregate transition between thenode computing devices 206(1) and 206(n) is performed.

As illustrated in the clustered network environment 200, node computingdevices 206(1)-206(n) can include various functional components thatcoordinate to provide a distributed storage architecture. For example,the node computing devices 206(1)-206(n) can include network modules214(1)-214(n) and disk modules 216(1)-216(n). Network modules214(1)-214(n) can be configured to allow the node computing devices206(1)-206(n) (e.g., network storage controllers) to connect with clientdevices 208(1)-208(n) over the storage network connections212(1)-212(n), for example, allowing the client devices 208(1)-208(n) toaccess data stored in the clustered network environment 200.

Further, the network modules 214(1)-214(n) can provide connections withone or more other components through the cluster fabric 204. Forexample, the network module 214(1) of node computing device 206(1) canaccess the data storage device 210(n) by sending a request via thecluster fabric 204 through the disk module 216(n) of node computingdevice 206(n) when the node computing device 206(n) is available.Alternatively, when the node computing device 206(n) fails, the networkmodule 214(1) of node computing device 206(1) can access the datastorage device 210(n) directly via the cluster fabric 204. The clusterfabric 204 can include one or more local and/or wide area computingnetworks (i.e., cloud networks) embodied as Infiniband, Fibre Channel(FC), or Ethernet networks, for example, although other types ofnetworks supporting other protocols can also be used.

Disk modules 216(1)-216(n) can be configured to connect data storagedevices 210(1)-210(n), such as disks or arrays of disks, SSDs, flashmemory, or some other form of data storage, to the node computingdevices 206(1)-206(n). Often, disk modules 216(1)-216(n) communicatewith the data storage devices 210(1)-210(n) according to the SANprotocol, such as SCSI or FCP, for example, although other protocols canalso be used. Thus, as seen from an operating system on node computingdevices 206(1)-206(n), the data storage devices 210(1)-210(n) can appearas locally attached. In this manner, different node computing devices206(1)-206(n), etc. may access data blocks, files, or objects throughthe operating system, rather than expressly requesting abstract files.

While the clustered network environment 200 illustrates an equal numberof network modules 214(1)-214(n) and disk modules 216(1)-216(n), otherexamples may include a differing number of these modules. For example,there may be a plurality of network and disk modules interconnected in acluster that do not have a one-to-one correspondence between the networkand disk modules. That is, different node computing devices can have adifferent number of network and disk modules, and the same nodecomputing device can have a different number of network modules thandisk modules.

Further, one or more of the client devices 208(1)-208(n) can benetworked with the node computing devices 206(1)-206(n) in the cluster,over the storage connections 212(1)-212(n). As an example, respectiveclient devices 208(1)-208(n) that are networked to a cluster may requestservices (e.g., exchanging of information in the form of data packets)of node computing devices 206(1)-206(n) in the cluster, and the nodecomputing devices 206(1)-206(n) can return results of the requestedservices to the client devices 208(1)-208(n). In one example, the clientdevices 208(1)-208(n) can exchange information with the network modules214(1)-214(n) residing in the node computing devices 206(1)-206(n)(e.g., network hosts) in the data storage apparatuses 202(1)-202(n).

In one example, the storage apparatuses 202(1)-202(n) host aggregatescorresponding to physical local and remote data storage devices, such aslocal flash or disk storage in the data storage devices 210(1)-210(n),for example. One or more of the data storage devices 210(1)-210(n) caninclude mass storage devices, such as disks of a disk array. The disksmay comprise any type of mass storage devices, including but not limitedto magnetic disk drives, flash memory, and any other similar mediaadapted to store information, including, for example, data and/or parityinformation. In an example, control of the aggregates stored within thedata storage devices 210(1)-210(n) may be switched between the nodecomputing devices 206(1) and 206(n) in the event of a disaster orplanned takeover. As provided herein, block allocation for persistentmemory during aggregate transition between the node computing devices206(1) and 206(n) is performed.

The aggregates include volumes 218(1)-218(n) in this example, althoughany number of volumes can be included in the aggregates. The volumes218(1)-218(n) are virtual data stores or storage objects that define anarrangement of storage and one or more filesystems within the clusterednetwork environment 200. Volumes 218(1)-218(n) can span a portion of adisk or other storage device, a collection of disks, or portions ofdisks, for example, and typically define an overall logical arrangementof data storage. In one example volumes 218(1)-218(n) can include storeduser data as one or more files, blocks, or objects that may reside in ahierarchical directory structure within the volumes 218(1)-218(n).

Volumes 218(1)-218(n) are typically configured in formats that may beassociated with particular storage systems, and respective volumeformats typically comprise features that provide functionality to thevolumes 218(1)-218(n), such as providing the ability for volumes218(1)-218(n) to form clusters, among other functionality. Optionally,one or more of the volumes 218(1)-218(n) can be in composite aggregatesand can extend between one or more of the data storage devices210(1)-210(n) and one or more of the cloud storage device(s) 236 toprovide tiered storage, for example, and other arrangements can also beused in other examples.

In one example, to facilitate access to data stored on the disks orother structures of the data storage devices 210(1)-210(n), a filesystemmay be implemented that logically organizes the information as ahierarchical structure of directories and files. In this example,respective files may be implemented as a set of disk blocks of aparticular size that are configured to store information, whereasdirectories may be implemented as specially formatted files in whichinformation about other files and directories are stored.

Data can be stored as files or objects within a physical volume and/or avirtual volume, which can be associated with respective volumeidentifiers. The physical volumes correspond to at least a portion ofphysical storage devices, such as the data storage devices 210(1)-210(n)(e.g., a Redundant Array of Independent (or Inexpensive) Disks (RAIDsystem)) whose address, addressable space, location, etc. does notchange. Typically the location of the physical volumes does not changein that the range of addresses used to access it generally remainsconstant.

Virtual volumes, in contrast, can be stored over an aggregate ofdisparate portions of different physical storage devices. Virtualvolumes may be a collection of different available portions of differentphysical storage device locations, such as some available space fromdisks, for example. It will be appreciated that since the virtualvolumes are not “tied” to any one particular storage device, virtualvolumes can be said to include a layer of abstraction or virtualization,which allows it to be resized and/or flexible in some regards.

Further, virtual volumes can include one or more logical unit numbers(LUNs), directories, Qtrees, files, and/or other storage objects, forexample. Among other things, these features, but more particularly theLUNs, allow the disparate memory locations within which data is storedto be identified, for example, and grouped as data storage unit. Assuch, the LUNs may be characterized as constituting a virtual disk ordrive upon which data within the virtual volumes is stored within anaggregate. For example, LUNs are often referred to as virtual drives,such that they emulate a hard drive, while they actually comprise datablocks stored in various parts of a volume.

In one example, the data storage devices 210(1)-210(n) can have one ormore physical ports, wherein each physical port can be assigned a targetaddress (e.g., SCSI target address). To represent respective volumes, atarget address on the data storage devices 210(1)-210(n) can be used toidentify one or more of the LUNs. Thus, for example, when one of thenode computing devices 206(1)-206(n) connects to a volume, a connectionbetween the one of the node computing devices 206(1)-206(n) and one ormore of the LUNs underlying the volume is created.

Respective target addresses can identify multiple of the LUNs, such thata target address can represent multiple volumes. The I/O interface,which can be implemented as circuitry and/or software in a storageadapter or as executable code residing in memory and executed by aprocessor, for example, can connect to volumes by using one or moreaddresses that identify the one or more of the LUNs.

Referring to FIG. 3 , node computing device 206(1) in this particularexample includes processor(s) 300, a memory 302, a network adapter 304,a cluster access adapter 306, and a storage adapter 308 interconnectedby a system bus 310. In other examples, the node computing device 206(1)comprises a virtual machine, such as a virtual storage machine. The nodecomputing device 206(1) also includes a storage operating system 312installed in the memory 302 that can, for example, implement a RAID dataloss protection and recovery scheme to optimize reconstruction of dataof a failed disk or drive in an array, along with other functionalitysuch as deduplication, compression, snapshot creation, data mirroring,synchronous replication, asynchronous replication, encryption, etc. Insome examples, the node computing device 206(n) is substantially thesame in structure and/or operation as node computing device 206(1),although the node computing device 206(n) can also include a differentstructure and/or operation in one or more aspects than the nodecomputing device 206(1). In an example, a file system may be implementedfor persistent memory.

The network adapter 304 in this example includes the mechanical,electrical and signaling circuitry needed to connect the node computingdevice 206(1) to one or more of the client devices 208(1)-208(n) overnetwork connections 212(1)-212(n), which may comprise, among otherthings, a point-to-point connection or a shared medium, such as a localarea network. In some examples, the network adapter 304 furthercommunicates (e.g., using TCP/IP) via the cluster fabric 204 and/oranother network (e.g. a WAN) (not shown) with cloud storage device(s)236 to process storage operations associated with data stored thereon.

The storage adapter 308 cooperates with the storage operating system 312executing on the node computing device 206(1) to access informationrequested by one of the client devices 208(1)-208(n) (e.g., to accessdata on a data storage device 210(1)-210(n) managed by a network storagecontroller). The information may be stored on any type of attached arrayof writeable media such as magnetic disk drives, flash memory, and/orany other similar media adapted to store information.

In the exemplary data storage devices 210(1)-210(n), information can bestored in data blocks on disks. The storage adapter 308 can include I/Ointerface circuitry that couples to the disks over an I/O interconnectarrangement, such as a storage area network (SAN) protocol (e.g., SmallComputer System Interface (SCSI), Internet SCSI (iSCSI), hyperSCSI,Fiber Channel Protocol (FCP)). The information is retrieved by thestorage adapter 308 and, if necessary, processed by the processor(s) 300(or the storage adapter 308 itself) prior to being forwarded over thesystem bus 310 to the network adapter 304 (and/or the cluster accessadapter 306 if sending to another node computing device in the cluster)where the information is formatted into a data packet and returned to arequesting one of the client devices 208(1)-208(n) and/or sent toanother node computing device attached via the cluster fabric 204. Insome examples, a storage driver 314 in the memory 302 interfaces withthe storage adapter to facilitate interactions with the data storagedevices 210(1)-210(n).

The storage operating system 312 can also manage communications for thenode computing device 206(1) among other devices that may be in aclustered network, such as attached to a cluster fabric 204. Thus, thenode computing device 206(1) can respond to client device requests tomanage data on one of the data storage devices 210(1)-210(n) or cloudstorage device(s) 236 (e.g., or additional clustered devices) inaccordance with the client device requests.

The file system module 318 of the storage operating system 312 canestablish and manage one or more filesystems including software code anddata structures that implement a persistent hierarchical namespace offiles and directories, for example. As an example, when a new datastorage device (not shown) is added to a clustered network system, thefile system module 318 is informed where, in an existing directory tree,new files associated with the new data storage device are to be stored.This is often referred to as “mounting” a filesystem.

In the example node computing device 206(1), memory 302 can includestorage locations that are addressable by the processor(s) 300 andadapters 304, 306, and 308 for storing related software application codeand data structures. The processor(s) 300 and adapters 304, 306, and 308may, for example, include processing elements and/or logic circuitryconfigured to execute the software code and manipulate the datastructures.

In the example, the node computing device 206(1) comprises persistentmemory 320. The persistent memory 320 comprises a plurality of pageswithin which data can be stored. The plurality of pages may be indexedby page block numbers.

The storage operating system 312, portions of which are typicallyresident in the memory 302 and executed by the processor(s) 300, invokesstorage operations in support of a file service implemented by the nodecomputing device 206(1). Other processing and memory mechanisms,including various computer readable media, may be used for storingand/or executing application instructions pertaining to the techniquesdescribed and illustrated herein. For example, the storage operatingsystem 312 can also utilize one or more control files (not shown) to aidin the provisioning of virtual machines.

In this particular example, the memory 302 also includes a moduleconfigured to implement the techniques described herein, including forexample block allocation for persistent memory during aggregatetransition as discussed above and further below.

The examples of the technology described and illustrated herein may beembodied as one or more non-transitory computer or machine readablemedia, such as the memory 302, having machine or processor-executableinstructions stored thereon for one or more aspects of the presenttechnology, which when executed by processor(s), such as processor(s)300, cause the processor(s) to carry out the steps necessary toimplement the methods of this technology, as described and illustratedwith the examples herein. In some examples, the executable instructionsare configured to perform one or more steps of a method described andillustrated later.

One embodiment of block allocation for persistent memory duringaggregate transition is illustrated by an exemplary method 400 of FIG. 4, which is further described in conjunction with system 500 of FIGS.5A-5G. A node (A) 502 may be paired with a node (B) 524, such as wherethe node (A) 502 and the node (B) 524 are a high availability node pairthat can provide takeover and giveback functionality in order to provideclients with non-disruptive access to data in the event one of the nodesfails. The node (A) 502 and/or the node (B) 524 may be implemented as aserver, a virtual machine (e.g., a storage virtual machine hosted withina cloud computing environment), software such as software as a service(SaaS), hardware, or a combination thereof.

The node (A) 502 may originally host and control an aggregate (A1) 518,an aggregate (A2) 520, and/or other local aggregates within which thenode (A) 502 may store data on behalf of client devices, as illustratedby FIG. 5A. The node (A) 502 may store at least some data of theaggregate (A1) 518 within a first local partition 506 of a persistentmemory (A) 504 of the node (A) 502 as aggregate (A1) data 510. Forexample, the persistent memory (A) 504 may provide lower latency andimproved performance compared to other storage available to the node (A)502, such as disk drives, cloud storage, solid state drives, etc. Thus,certain data may be stored within the persistent memory (A) 504 such asrecently accessed data, frequently accessed data, data predicted to beaccessed within a threshold time span, etc. The node (A) 502 may storeat least some data of the aggregate (A2) 520 within the first localpartition 506 of the persistent memory (A) 504 as aggregate (A2) data512. During normal operation, the first local partition 506 may not bepartitioned, such that there is no hard partition to separate/divide thefirst local partition 506 for separately storing and partitioning theaggregate (A1) data 510 from the aggregate (A2) data 512.

The node (B) 524 may originally host and control an aggregate (B1) 542,an aggregate (B2) 540, and/or other local aggregates within which thenode (B) 524 may store data on behalf of client devices. The node (B)524 may store at least some data of the aggregate (B1) 542 within asecond local partition 528 of a persistent memory (B) 526 of the node(B) 524 as aggregate (B1) data 532. For example, the persistent memory(B) 526 may provide lower latency and improved performance compared toother storage available to the node (B) 524, such as disk drives, cloudstorage, solid state drives, etc. Thus, certain data may be storedwithin the persistent memory (B) 526 such as recently accessed data,frequently accessed data, data predicted to be accessed within athreshold time span, etc. The node (B) 524 may store at least some dataof the aggregate (B2) 540 within the second local partition 528 of thepersistent memory (B) 526 as aggregate (B2) data 534. During normaloperation, the second local partition 528 may not be partitioned, suchthat there is no hard partition to separate/divide the second localpartition 528 for separately storing and partitioning the aggregate (B1)data 532 from the aggregate (B2) data 534.

In order to provide client with non-disruptive access to data within theaggregates hosted by the nodes, the nodes need access to up-to-date dataof the other nodes, such as data stored within a persistent memory of apartner node. Accordingly, the persistent memory (A) 504 of the node (A)502 comprises a first remote partition 508. The aggregate (B1) data 532is mirrored from the second local partition 528 of the persistent memory(B) 526 of the node (B) 524 into the first remote partition 508 of thepersistent memory (A) 504 of the node (A) 502 as mirrored aggregate (B1)data 514. The aggregate (B2) data 534 is mirrored from the second localpartition 528 of the persistent memory (B) 526 of the node (B) 524 intothe first remote partition 508 of the persistent memory (A) 504 of thenode (A) 502 as mirrored aggregate (B2) data 516.

Similarly, the persistent memory (B) 526 of the node (B) 524 comprises asecond remote partition 530. The aggregate (A1) data 510 is mirroredfrom the first local partition 506 of the persistent memory (A) 504 ofthe node (A) 502 into the second remote partition 530 of the persistentmemory (B) 526 of the node (B) 524 as mirrored aggregate (A1) data 536.The aggregate (A2) data 512 is mirrored from the first local partition506 of the persistent memory (A) 504 of the node (A) 502 into the secondremote partition 530 of the persistent memory (B) 526 of the node (B)524 as mirrored aggregate (A2) data 538.

The node (A) 502 may maintain various metadata information 522 regardingthe persistent memory (A) 504. In an embodiment, the metadatainformation 522 may indicate whether a page within the persistent memory(A) 504 is reserved for use by an aggregate. In another embodiment, thenode (A) 502 may maintain free lists of free pages within the firstlocal partition 506 and the first remote partition 508 that areavailable to allocate for storing data of the aggregates (e.g., a listof page block numbers indexing free pages that do not comprise datareferenced by at least one of an active file system or snapshots of theactive file system).

As the node (A) 502 processes I/O directed to the aggregate (A1) 518and/or the aggregate (A2) 520 using the first local partition 506, dataassociated with the I/O (e.g., data being written to the aggregate (A1)518 and/or the aggregate (A2) 520) is mirrored into the second remotepartition 530 of the persistent memory (B) 526 of the node (B) 524.Thus, if the node (A) 502 fails, the node (B) 524 will have access toup-to-date data of the aggregate (A1) 518 and the aggregate (A2) 520within the second remote partition 530 for taking over subsequentprocessing I/O directed to the aggregate (A1) 518 and the aggregate (A2)520 in place of the failed node (A) 502.

Similarly, as the node (B) 524 processes I/O directed to the aggregate(B1) 542 and/or the aggregate (B2) 540 using the second local partition532, data associated with the I/O (e.g., data being written to theaggregate (B1) 542 and/or the aggregate (B2) 540) is mirrored into thefirst remote partition 508 of the persistent memory (A) 504 of the node(A) 502. Thus, if the node (B) 524 fails, the node (A) 502 will haveaccess to up-to-date data of the aggregate (B1) 542 and the aggregate(B2) 540 within the first remote partition 508 for taking oversubsequent processing I/O directed to the aggregate (B1) 542 and theaggregate (B2) 540 in place of the failed node (B) 524.

FIG. 5B illustrates an embodiment of the node (B) 524 failing 550. In anembodiment, the node (A) 502 may detect the failure 550 of the node (B)524 through various mechanisms, such as by detecting a loss of aheartbeat signal otherwise generated by the node (B) 524 during normaloperation of the node (B) 524. It may be appreciated that variousmechanism may be used to determine whether a node has failed or isoperational. In response to detecting the failure 550 of the node (B)524, the node (A) 502 performs a takeover procedure to take over controlof the aggregate (B1) 542 and/or the aggregate (B2) 540 from the node(B) 524, as illustrated by FIG. 5C. Because the node (B) 524 has failed,the node (A) 502 will take control of the aggregate (B1) 542 and theaggregate (B2) 540 so that the node (A) 502 can process I/O directed tothe aggregate (B1) 542 and the aggregate (B2) 540 that would otherwisehave been processed by the node (B) 524 during normal operation. As partof the takeover procedure, the node (A) 502 evaluates the mirroredaggregate (B1) data 514 and the mirrored aggregate (B2) data 516 withinthe first remote partition 508 of the persistent memory (A) 504 to builda free pages list of free pages (e.g., a list of page block numbers ofthe free pages) of the first remote partition 508 that are available forsubsequent allocation by the node (A) 502 for storing data of I/Odirected to the aggregate (B1) 542 and/or the aggregate (B2) 540.

Once the takeover procedure has completed, the node (A) 502 processesI/O directed to the aggregate (A1) 518 using the first local partition506 of the persistent memory (A) 504 of the node (A) 502. The node (A)502 processes I/O directed to the aggregate (A2) 520 using the firstlocal partition 506 of the persistent memory (A) 504 of the node (A)502. The node (A) 502 processes I/O directed to the aggregate (B1) 542using the first remote partition 508 of the persistent memory (A) 504 ofthe node (A) 502. The node (A) 502 processes I/O directed to theaggregate (B2) 540 using the first remote partition 508 of thepersistent memory (A) 504 of the node (A) 502. In this way, theaggregate (A1) data 510, the aggregate (A2) data 512, the aggregate (B1)data 514, and/or the aggregate (B2) data 516 may change over time basedupon the node (A) 502 processing write commands, delete commands, and/orother commands that modify such data.

At some point in time, the node (B) 524 recovers from the failure 550,as illustrated by FIG. 5D. At 402 (of FIG. 4 's exemplary method 400), adetermination is made that the node (A) 502 is to transition control ofthe aggregate (B1) 542 and/or the aggregate (B2) 540 back from the node(A) 502 to the node (B) 524. While embodiments of FIG. 4 's method 400are described with respect to a giveback procedure, they may also applyto takeover procedures. However, discussion of FIG. 4 's method 400 willbe done with respect to a giveback procedure for sake of demonstration.Various indicators may trigger the determination that the node (A) 502is to transition control of the aggregate (B1) 542 and/or the aggregate(B2) 540 to the node (B) 524. In an embodiment, the node (B) 524 maytransmit a request to the node (A) 502 to perform a giveback procedureof the aggregate (B1) 542 and/or the aggregate (B2) 540. In anotherembodiment, the node (A) 502 may detect that the node (B) 524 hasrecovered from the failure 550, and thus inquire with node (B) 524 as towhether a giveback procedure of the aggregate (B1) 542 and/or theaggregate (B2) 540 should be performed. In this way, the node (A) 502may determine that the giveback procedure is to be implemented to returncontrol of the aggregate (B1) 542 and/or the aggregate (B2) 540 from thenode (A) 502 to the node (B) 524.

Once the node (B) 524 has recovered from the failure 550 (e.g., beforethe giveback procedure has commenced or completed), current data of themirrored aggregate (B1) data 514 and/or the mirrored aggregate (B2) data516 is resynchronized from the first remote partition 508 of thepersistent memory (A) 504 of the node (A) 502 into the second localpartition 528 of the persistent memory (B) 526 of the node (B) 524. Inan embodiment, a byte-by-byte resynchronization is performed toresynchronize changes made to the aggregate (B1) 542 and/or theaggregate (B2) 540 while controlled by the node (A) 502 to the secondlocal partition 528 of the persistent memory (B) 526 of the node (B)524. In this way, a resynchronization process is performed toresynchronize current data of the mirrored aggregate (B1) data 514and/or the mirrored aggregate (B2) data 516 from the first remotepartition 508 of the persistent memory (A) 504 of the node (A) 502 intothe second local partition 528 of the persistent memory (B) 526 of thenode (B) 524.

Furthermore, mirroring of incoming I/O operations directed to theaggregate (B1) 541 and/or the aggregate (B2) 540 is performed (e.g.,based on the node (A) 502 knowing that node (B) 524 is recovered). Inthis way, the mirrored aggregate (B1) data 514 of the aggregate (B1) 542and/or the mirrored aggregate (B2) data 516 of the aggregate (B2) 540being modified by I/O operations being processed by the node (A) 502using the first remote partition 508 of the persistent memory (A) 504 ofthe node (A) 502 is being mirrored to the second local partition 528 ofthe persistent memory (B) 526 of the node (B) 524. For example, the node(A) 502 may receive a write operation from a client device before thegiveback procedure has completed. The write operation may target theaggregate (B1) 542 in order to write data to the aggregate (B1) 542.Because the node (A) 502 has control over the aggregate (B1) 542, thenode (A) 502 writes the data to the mirrored aggregate (B1) data 514within the first remote partition 508 of the persistent memory (A) 504of the node (A) 502. The node (A) 502 also mirrors that data into theaggregate (B1) data 532 within the second local partition 528 of thepersistent memory (B) 526 of the node (B) 524 as part of processing thewrite operation. In this way, data of incoming operations is mirrored tothe second local partition 528 of the persistent memory (B) 526 of thenode (B) 524 (e.g., before the giveback procedure has commenced orcompleted).

Once the node (A) 502 has determined that the giveback procedure is tobe implemented to give back control of the aggregate (B1) 542 and/or theaggregate (B2) 540 from the node (A) 502 to the node (B) 524, the node(A) 502 may initiate giveback of the aggregate (B1) 542 and/or theaggregate (B2) 540 one at a time. In an embodiment, the node (A) 502initiates giveback of the aggregate (B1) 542 to the node (B) 524. Aspart of the giveback, soft partitions (e.g., the allocation/reservationof certain free pages for use by the aggregate (B1) 542 and theallocation/reservation of different free pages for use by the aggregate(B2) 540) are created in the event control of one of the aggregates doesnot get transitioned to the node (B) 524, and thus the node (B) 524would be serving I/O for that aggregate while the node (A) 502 would beserving I/O for the other aggregate. In that event, each node will nowallocate different free pages to store data of the aggregate that nodecontrols, thus avoiding instances of data corruption and loss where eachnode could otherwise allocate the same free page to store different dataof the different aggregates.

At 404, the node (A) 502 allocates a portion of available free storagespace from the first remote partition 508 of the persistent memory (A)504 of the node (A) 502. For example, the persistent memory (A) 504 maybe comprised of pages within which data can be stored. The pages may beindexed by page block numbers (e.g., a first page having a first pageblock number, a second page having a second page block number, etc.). Apage may be a free page that is available for storing data, such asbecause the free page does not comprise data or comprises data that isno longer referenced by an active file system and snapshots of theactive file system. A page may be a used page that is unavailable forstoring data, such as because the used page comprises data currentlyreferenced by an active file system and/or one or more snapshots of theactive file system.

The portion of available free storage space may be allocated as a set offree pages within the first remote partition 508 of the persistentmemory (A) 504 of the node (A) 502. The set of free pages may comprisefree pages that reserved for subsequent allocation and use for storingdata associated with the aggregate (B1) 542 within the first remotepartition 508 of the persistent memory (A) 504 of the node (A) 502. Thenode (A) 502 may determine what percentage of free pages within thefirst remote partition 508 to allocate and reserve as the portion ofavailable free storage space for subsequent use to store data of theaggregate (B1) 542 based upon various factors such as how many otheraggregates are using the first remote partition 508 for storing data. Inan example, free storage space may be allocated evenly across allaggregates using the first remote partition 508. In another example, thepercentage of free pages allocated for the aggregate (B1) 542 may bebased upon historic storage space utilization by the aggregate (B1) 542(e.g., if only a small percentage is historically used by the aggregate(B1) 542, then a relatively small percentage of the available free pagesmay be allocated/reserved for use by the aggregate (B1) 542), predictedutilization, etc. The set of free pages allocated/reserved for use bythe aggregate (B1) 542 are removed from a free pages list maintained bythe node (A) 502 of free pages available for use by other aggregates.

In an embodiment, because the set of free pages is merelyallocated/reserved during the transition of control of aggregates fromthe node (A) 502 to the node (B) 524, the first remote partition 508 andthe second local partition 528 have a temporary soft partition of theset of free pages for the aggregate (B1) 540. In an embodiment, thissoft partition can be removed once control of the aggregate(s) has beenfully transferred and onlined (e.g., made available for access by clientdevices) by the node (B) 524.

Implementing soft partitions, instead of hard partitions, for data ofaggregates using the local partitions and remote partitions of thepersistent memory (A) 504 of the node (A) 502 and the persistent memory(B) 526 of the node (B) 524 allows for the local partitions and theremote partitions to be sized and resized based upon variousconsiderations (e.g., arbitrarily sized, sized/resized based uponcurrent/historic/predicted utilization, etc.). Furthermore, implementingsoft partitions, instead of hard partitions, for data of aggregatesusing the local partitions and remote partitions of the persistentmemory (A) 504 of the node (A) 502 and the persistent memory (B) 526 ofthe node (B) 524 allows for any number of aggregates to be supported.Thus, a node may store data of any number of aggregates within a localpartition and/or a remote partition of persistent memory of the node. Inan embodiment, because a soft partition is merely implemented for thelocal partitions and remote partitions of the persistent memories duringa transition window of transitioning control of aggregates betweennodes, no soft partition may be used outside of the transition window(e.g., the first local partition 506 is not partitioned for use bycertain aggregates, the first remote partition 508 is not partitionedfor use by certain aggregates, the second local partition 528 is notpartitioned for use by certain aggregates, and the second remotepartition 530 is not partitioned for use by certain aggregates whenaggregates are not being transitioned between nodes). In an embodiment,once all aggregates have been transitioned, then any soft partitions maybe removed.

Once the portion of available free storage space of the first remotepartition 508 of the persistent memory (A) 504 of the node (A) 502 hasbeen allocated/reserved as allocated pages for the aggregate (B1) 542,the node (A) 502 may update the metadata information 522 as updatedmetadata information 552 for the aggregate (B1) 542 to indicate that theallocated pages are allocated/reserved for use in storing data of theaggregate (B1) 542, at 406. For example, the allocated pages that areallocated/reserved for the aggregate (B1) 542 are tagged with anidentifier of the aggregate (B1) 542 to reserve the allocated pages forthe aggregate (B1) 542 (e.g., page block numbers of the allocated pagesmay be tagged with the identifier). In this way, the updated metadatainformation 552 for the aggregate (B1) 542 comprises page block numbersof the allocated pages that are tagged with the identifier of theaggregate (B1) 542.

At 408, the node (A) 502 mirrors the updated metadata information 552for the aggregate (B1) 542 to the node (B) 524. For example, the updatedmetadata information 552 is transmitted from the node (A) 502 to thenode (B) 524, as illustrated by FIG. 5D. In this way, the node (B) 524may store the updated metadata information 552 for the aggregate (B1)542 so that the node (B) 524 can identify what free pages within thesecond local partition 528 of the persistent memory (B) 526 of the node(B) 524 to reserve for use by the aggregate (B1) 542 once control of theaggregate (B1) 542 has been transitioned form the node (A) 502 to thenode (B) 524. In this way, the node (B) 524 may construct a free pageslist for the aggregate (B1) 542 (e.g., a list of page block numbers offree pages that are allocated/reserved for use by the node (B) 524 forstoring data of the aggregate (B1) 542) by adding free pages (e.g., pageblock numbers of the free pages) tagged with the identifier of theaggregate (B1) 542 into the free pages list for the aggregate (B1) 542and excluding other pages from the free pages list for the aggregate(B1) 542. Thus, the allocated pages, tagged with the identifier of theaggregate (B1) 542 within the updated metadata 522 for the aggregate(B1) 542, are added into the free pages list as being allocated/reservedfor use to store data of the aggregate (B1) 542 within the second localpartition 528 of the persistent memory (B) 526 of the node (B) 524. Inthis way, both the node (A) 502 and the node (B) 524 have reserved thesame free pages for use in storing data of the aggregate (B1) 542.

New block allocations for the aggregate (B1) 542 (e.g., allocations offree pages to store data of the aggregate (B1) 542) are directed to theallocated pages within the free pages list that were added to the freepages list based upon the allocated pages being tagged with theidentifier of the aggregate (B1) 542 (e.g., until completion of thegiveback of all aggregates). Because both the node (A) 502 and the node(B) 524 have the same allocated pages that are reserved for use by theaggregate (B1) 542 to store data of the aggregate (B1) 542 into thesecond local partition 528 of the persistent memory (B) 526 of the node(B) 524 and into the first remote partition 508 of the persistent memory(A) 508 of the node (A) 502, data corruption and loss is avoided. Datacorruption is avoided where the node (A) 502 and the node (B) 524 couldotherwise allocate the same page having the same page block number tostore different data (e.g., node (A) 502 could store data of theaggregate (B2) 540 into a free page having a same page block number as afree page at which node (B) 524 stores data of the aggregate (B1) 524after control of the aggregate (B1) 542 has been transitioned to thenode (B) 524) if the node (A) 502 and the node (B) 524 did not have thesame allocated pages for the aggregate (B1) 542. Data corruption wouldresult because the first remote partition 508 of the persistent memory(A) 504 of the node (A) 502 and the second local partition 528 of thepersistent memory (B) 526 of the node (B) 524 are to be mirrors of oneanother comprising the exact same data. Either the free page within thefirst remote partition 508 and the free page within the second localpartition 528 will comprise different data, or due to mirroring one ofthe free pages will be overwritten and thus result in data loss.However, since both the node (A) 502 and the node (B) 524 have the sameallocated pages for the aggregate (B1) 542, data corruption and loss isavoided.

At 410, control of the aggregate (B1) 542 is given back 554 from thenode (A) 502 to the node (B) 524, as illustrated by FIG. 5E. In anembodiment, control of the aggregate (B1) 542 is given back 554 to thenode (B) 524 upon confirmation that the node (B) 524 has constructed thefree pages list for the aggregate (B1) 542 based upon the updatedmetadata information 552 for the aggregate (B1) 542. Once node (B) 524has control of the aggregate (B1) 542, the node (B) 524 will activelyserve I/O directed to the aggregate (B1) 542 using the allocated pages,within the free pages list, of the second local partition 528 of thepersistent memory (B) 526 of the node (B) 524. Data is also activelymirrored from the second local partition 528 of the persistent memory(B) 526 of the node (B) 524 to the first remote partition 508 of thepersistent memory (A) 504 of the node (A) 502 (e.g., data written to aparticular page within the second local partition 528 will be mirroredto a corresponding same page within the first remote partition 508).

Once control of the aggregate (B1) 542 has successfully been transferredfrom the node (A) 502 to the node (B) 524, the node (A) 502 mayinitiated transfer of control of the aggregate (B2) 540 to the node (B)524, as illustrated by FIGS. 5F and 5G. Transfer of control of theaggregate (B2) 540 may be performed in a similar manner as how controlof the aggregate (B1) 542 was transferred to the node (B) 524. Inparticular, the node (A) 502 may allocate a second portion of availablefree storage space within the first remote partition 508 of thepersistent memory (A) 504 of the node (A) 502 as second allocated pagesthat are allocated/reserved for the aggregate (B2) 540. The secondallocated pages comprise free pages within the first remote partition508 that are reserved for subsequent use to store data of the aggregate(B2) 540 by the node (A) 502. The second allocated pages will bedifferent than the allocated pages that were allocated/reserved for theaggregate (B1) 542, and thus data corruption is avoided because the node(A) 502 will not allocate the same free page for use by the aggregate(B2) 540 (e.g., if control of the aggregate (B2) 540 is retained by thenode (A) 502 for serving subsequent I/O directed to the aggregate (B2)540) as a corresponding free page having a same page block number thatis allocated by the node (B) 524 to store data of the aggregate (B1)542.

The node (A) 502 updates metadata information associated with theaggregate (B2) 540 as updated metadata information (B2) 560 for theaggregate (B2) 540. The updated metadata information (B2) 560 comprisesthe second allocated pages (e.g., page block numbers of the secondallocated pages) tagged with a second identifier of the aggregate (B2)540. In this way, the second allocated pages are reserved for subsequentallocation to store data of the aggregate (B2) 540 within the firstremote partition 508 of the persistent memory (A) 504 of the node (A)502. The allocated pages are removed from the free pages list maintainedby the node (A) 502 for the first remote partition 508. The updatedmetadata information (B2) 560 is mirrored from the node (A) 502 to thenode (B) 524, as illustrated by FIG. 5F. The node (B) 524 constructs afree pages list for the aggregate (B2) 540 based upon the updatedmetadata information (B2) 560 for the aggregate (B2) 540 by includingpage block numbers of the second allocated pages tagged with the secondidentifier within the updated metadata information (B2) 560. Once thenode (B) 524 has reserved the second allocated pages for the aggregate(B2) 540, the node (A) 502 transitions control of the aggregate (B2) 540to the node (B) 524 by performing a giveback 570 of the aggregate (B2)540, as illustrated by FIG. 5G. In this way, the node (B) 524 activelyprocesses I/O directed to the aggregate (B2) 540 using the second localpartition 528 of the persistent memory (B) 526 of the node (B) 524,while mirroring data of the I/O to the first remote partition 508 of thepersistent memory (A) 504 of the node (A) 502.

Once the transition of the aggregates has completed, the soft partitionof the local partitions and the remote partitions may be removed. Thesoft partitions (e.g., the allocation/reservation of certain free pagesfor use by the aggregate (B1) 542 and the allocation/reservation ofdifferent free pages for use by the aggregate (B2) 540) were created inthe event control of one of the aggregates did not get transitioned tothe node (B) 524, and thus the node (B) 524 would be serving I/O forthat aggregate while the node (A) 502 would be serving I/O for the otheraggregate. In that event, each node will now allocate different freepages to store data of the aggregate that node controls, thus avoidinginstances of data corruption and loss where each node could otherwiseallocate the same free page to store different data of the differentaggregates.

In an embodiment, before the transitioning of the aggregates from thenode (A) 502 to the node (B) 524 has successfully completed, availablefree spaces within the persistent memories of the node (A) 502 and thenode (B) 524 may be monitored in the event there is a lack of free spacefor processing an incoming operation. If the incoming operation targetsan aggregate (e.g., aggregate (B2) 540 while still controlled by thenode (A) 520) for which there is a lack of available free space (e.g., alack of free pages allocated to the aggregate (B2) 540 from the firstremote partition 508) to process the incoming operation, then theincoming operation is suspended, such as queued for subsequentprocessing once adequate resources become available. A pace at which ascavenger process reclaims unused space (e.g., frees pages as availablefree pages because those pages are no longer referenced by the activefile system and/or snapshots of the active file system) may be increasedin response to suspending the incoming operation. In this way, availablefree pages allocated/reserved for the aggregate (B2) 540 may becomeavailable more quickly.

Block allocation for persistent memory during aggregate transition hasbeen described, with respect to FIGS. 5A-5G, in relation to the node (A)502 performing a giveback procedure after the node (B) 524 recoveredfrom the failure 550. It may be appreciated that block allocation forpersistent memory during aggregate transition can be performed in asimilar/same manner for other scenarios. For example, block allocationfor persistent memory during aggregate transition may be performedduring a takeover, such as a planned takeover where a first node is totakeover aggregates one by one from a second node that is stilloperational. For each aggregate whose control is being transitioned fromthe second node to the first node, the second node may allocate pageswithin persistent memory of the second node as being reserved for anaggregate being transitioned to the first node. Metadata information forthe allocated pages is updated with an identifier of the aggregate tocreate updated metadata information that is mirrored to the first node.Once the first node has allocated/reserved the allocated pages from apersistent memory of the first node, the second node transitions controlof the aggregate to the first node. In this way, block allocation forpersistent memory during aggregate transition may be performed for thetakeover procedure in a same/similar manner as for the givebackprocedure.

Still another embodiment involves a computer-readable medium 600comprising processor-executable instructions configured to implement oneor more of the techniques presented herein. An example embodiment of acomputer-readable medium or a computer-readable device that is devisedin these ways is illustrated in FIG. 6 , wherein the implementationcomprises a computer-readable medium 608, such as a compactdisc-recordable (CD-R), a digital versatile disc-recordable (DVD-R),flash drive, a platter of a hard disk drive, etc., on which is encodedcomputer-readable data 606. This computer-readable data 606, such asbinary data comprising at least one of a zero or a one, in turncomprises processor-executable computer instructions 604 configured tooperate according to one or more of the principles set forth herein. Insome embodiments, the processor-executable computer instructions 604 areconfigured to perform a method 602, such as at least some of theexemplary method 400 of FIG. 4 , for example. In some embodiments, theprocessor-executable computer instructions 604 are configured toimplement a system, such as at least some of the exemplary system 500 ofFIGS. 5A-5G, for example. Many such computer-readable media arecontemplated to operate in accordance with the techniques presentedherein.

In an embodiment, the described methods and/or their equivalents may beimplemented with computer executable instructions. Thus, in anembodiment, a non-transitory computer readable/storage medium isconfigured with stored computer executable instructions of analgorithm/executable application that when executed by a machine(s)cause the machine(s) (and/or associated components) to perform themethod. Example machines include but are not limited to a processor, acomputer, a server operating in a cloud computing system, a serverconfigured in a Software as a Service (SaaS) architecture, a smartphone, and so on. In an embodiment, a computing device is implementedwith one or more executable algorithms that are configured to performany of the disclosed methods.

It will be appreciated that processes, architectures and/or proceduresdescribed herein can be implemented in hardware, firmware and/orsoftware. It will also be appreciated that the provisions set forthherein may apply to any type of special-purpose computer (e.g., filehost, storage server and/or storage serving appliance) and/orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings herein can be configured to a variety of storage systemarchitectures including, but not limited to, a network-attached storageenvironment and/or a storage area network and disk assembly directlyattached to a client or host computer. Storage system should thereforebe taken broadly to include such arrangements in addition to anysubsystems configured to perform a storage function and associated withother equipment or systems.

In some embodiments, methods described and/or illustrated in thisdisclosure may be realized in whole or in part on computer-readablemedia. Computer readable media can include processor-executableinstructions configured to implement one or more of the methodspresented herein, and may include any mechanism for storing this datathat can be thereafter read by a computer system. Examples of computerreadable media include (hard) drives (e.g., accessible via networkattached storage (NAS)), Storage Area Networks (SAN), volatile andnon-volatile memory, such as read-only memory (ROM), random-accessmemory (RAM), electrically erasable programmable read-only memory(EEPROM) and/or flash memory, compact disk read only memory (CD-ROM)s,CD-Rs, compact disk re-writeable (CD-RW)s, DVDs, cassettes, magnetictape, magnetic disk storage, optical or non-optical data storage devicesand/or any other medium which can be used to store data.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter defined in the appended claims is not necessarilylimited to the specific features or acts described above. Rather, thespecific features and acts described above are disclosed as exampleforms of implementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated given the benefit ofthis description. Further, it will be understood that not all operationsare necessarily present in each embodiment provided herein. Also, itwill be understood that not all operations are necessary in someembodiments.

Furthermore, the claimed subject matter is implemented as a method,apparatus, or article of manufacture using standard application orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as used herein isintended to encompass a computer application accessible from anycomputer-readable device, carrier, or media. Of course, manymodifications may be made to this configuration without departing fromthe scope or spirit of the claimed subject matter.

As used in this application, the terms “component”, “module,” “system”,“interface”, and the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware, software, or software in execution. For example, a componentincludes a process running on a processor, a processor, an object, anexecutable, a thread of execution, an application, or a computer. By wayof illustration, both an application running on a controller and thecontroller can be a component. One or more components residing within aprocess or thread of execution and a component may be localized on onecomputer or distributed between two or more computers.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB and/or both A and B. Furthermore, to the extent that “includes”,“having”, “has”, “with”, or variants thereof are used, such terms areintended to be inclusive in a manner similar to the term “comprising”.

Many modifications may be made to the instant disclosure withoutdeparting from the scope or spirit of the claimed subject matter. Unlessspecified otherwise, “first,” “second,” or the like are not intended toimply a temporal aspect, a spatial aspect, an ordering, etc. Rather,such terms are merely used as identifiers, names, etc. for features,elements, items, etc. For example, a first set of information and asecond set of information generally correspond to set of information Aand set of information B or two different or two identical sets ofinformation or the same set of information.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. A system comprising: a first node comprising afirst persistent memory, wherein the first persistent memory includes afirst local partition and a first remote partition, wherein the firstnode utilizes the first local partition to service client I/O, andwherein the first node is configured to: mirror data from pages withinthe first local partition to a second remote partition of a secondpersistent memory of a second node; recover from a failure where thesecond node took over control for the first node during the failure ofthe first node, wherein the second node services subsequent client I/Oon behalf of the first node using the data mirrored from the first nodeto the second remote partition of the second persistent memory of thesecond node; and execute a resynchronization process to synchronizechanges made to the second remote partition by the subsequent client I/Oto the first local partition of the first persistent memory of the firstnode.
 2. The system of claim 1, wherein the first node: in response tothe resynchronization process completing, performs a giveback procedurefor the second node to give back control to the first node.
 3. Thesystem of claim 1, wherein the first node: stores mirrored data receivedfrom the second node into pages of the first remote partition of thefirst persistent memory.
 4. The system of claim 1, wherein the firstnode: executes a byte by byte resynchronization to synchronize thechanges to the first local partition.
 5. The system of claim 1, whereincontrol of an aggregate is transitioned to the second node in responseto the first node failing, and wherein the first node: performs theresynchronization process to synchronize changes made to the aggregatewhile controlled by the second node.
 6. The system of claim 1, whereinthe first node: executes a scavenger to reclaim pages as available pagesbased upon the pages no longer being referenced by an active filesystem.
 7. The system of claim 1, wherein the first node: executes ascavenger to reclaim pages as available pages based upon the pages nolonger being referenced by snapshots of an active file system.
 8. Thesystem of claim 1, wherein page block numbers and data of pages withinthe second remote partition mirrors page block numbers and data of pageswithin the first local partition.
 9. The system of claim 1, wherein thefirst node: implements a soft partition for the first persistent memoryto partition the first persistent memory into a number of partitions foran arbitrary number of aggregates.
 10. The system of claim 1, whereinthe first node: implements a soft partition for the first persistentmemory to partition the first persistent memory into the first localpartition and the first remote partition having arbitrary sizes.
 11. Thesystem of claim 1, wherein the first node: limits new allocations, ofpages from the first remote partition for an aggregate, to allocatedpages having page block numbers tagged with an aggregate identifier. 12.The system of claim 1, wherein allocated pages within the first remotepartition maintained by the first node for an aggregate have same pageblock numbers as pages within a second local partition allocated to theaggregate by the second node, and wherein data within the pages withinthe second local partition are mirrored to the allocated pages havingthe same page block numbers.
 13. A method comprising: maintaining pagesof data within a first persistent memory of a first node, wherein thefirst persistent memory includes a first local partition and a firstremote partition, wherein the first node utilizes the first localpartition to service client I/O; mirroring data from pages within thefirst local partition to a second remote partition of a secondpersistent memory of a second node; recovering from a failure where thesecond node took over control for the first node during the failure ofthe first node, wherein the second node services subsequent client I/Oon behalf of the first node using the data mirrored from the first nodeto the second remote partition of the second persistent memory of thesecond node; and executing a resynchronization process to synchronizechanges made to the second remote partition by the subsequent client I/Oto the first local partition of the first persistent memory of the firstnode.
 14. The method of claim 13, comprising: in response to theresynchronization process completing, performing a giveback procedurefor the second node to give back control to the first node.
 15. Themethod of claim 13, comprising: storing mirrored data received from thesecond node into pages of the first remote partition of the firstpersistent memory.
 16. The method of claim 13, comprising: executing abyte by byte resynchronization to synchronize the changes to the firstlocal partition.
 17. The method of claim 13, wherein control of anaggregate is transitioned to the second node in response to the firstnode failing, and wherein the method comprises: performing theresynchronization process to synchronize changes made to the aggregatewhile controlled by the second node.
 18. The method of claim 13,comprising: executing a scavenger to reclaim pages as available pagesbased upon the pages no longer being referenced by an active filesystem.
 19. The method of claim 13, comprising: executing a scavenger toreclaim pages as available pages based upon the pages no longer beingreferenced by snapshots of an active file system.
 20. A non-transitorymachine readable medium comprising instructions for performing a method,which when executed by a machine, causes the machine to: maintain pagesof data within a first persistent memory of a first node, wherein thefirst persistent memory includes a first local partition and a firstremote partition, wherein the first node utilizes the first localpartition to service client I/O; mirror data from pages within the firstlocal partition to a second remote partition of a second persistentmemory of a second node; recover from a failure where the second nodetook over control for the first node during the failure of the firstnode, wherein the second node services subsequent client I/O on behalfof the first node using the data mirrored from the first node to thesecond remote partition of the second persistent memory of the secondnode; and execute a resynchronization process to synchronize changesmade to the second remote partition by the subsequent client I/O to thefirst local partition of the first persistent memory of the first node.